Blackbaud does not make specific recommendations on tracking this information. Refer to our Support Forums, to ask other clients how they handle this at their organization.  One consideration to keep in mind would be whether you would need to query specifically on, for example, Mothers, Grandmothers, Daughters, etc. versus Parent, Grandparent, Child.  For example, you wish to invite the Mothers and Grandmothers to a Mother's Day event.